Overview: What is soldering and when should you use it?

Soldering is a process in which two or more metal items are joined together by melting and then flowing a filler metal into the joint—the filler metal having a relatively low melting point.

Soldering is used to form a permanent connection between electronic components.

The metal to be soldered is heated with a soldering iron and then solder is melted into the connection.

Only the solder melts, not the parts that are being soldered.

Solder is a metallic "glue" that holds the parts together and forms a connection that allows electrical current to flow.

You can use a solderless breadboard to make test circuits, but if you want your circuit to last for more than a few days, you will want to solder the components together.

Materials and Equipment

A soldering iron

A soldering iron is used to heat the connections to be soldered.

For electronic circuits, you should use a 25- to 40-watt (W) soldering iron.

Higher wattage soldering irons are not necessarily hotter; they are just able to heat larger components. A 40-W soldering iron makes joints faster than a 25-W soldering iron does.

A soldering iron can be purchased at hardware stores and at most large department stores.

Rosin core solder

Solder has a lower melting point than the metals that are being connected do. The solder melts when it is heated by the soldering iron, but the metals being joined will not melt.

The rosin core acts as a flux. It prevents oxidation of the metals that are being connected, and enhances the ability of the solder to "wet" the surfaces that are being joined.

Solder that is used to join copper pipes has an acid core, which is appropriate for pipes, but will corrode electronic connections. Use solder that has a rosin core.

For most electronics work, a solder with a diameter of 0.75 millimeters (mm) to 1.0 mm is best. Thicker solder might make soldering small joints difficult and also increases the chances of creating solder bridges between copper pads that are not meant to be connected.

An alloy of 60/40 (60% tin, 40% lead) is used for most electronics work, but lead-free solders are available as well.

Stand on which to hold the hot soldering iron

There are a variety of stands available. It is important to always keep the hot iron in its stand when not in use.

Sponge

The damp sponge is used to clean the tip of the iron.

Figure 1. Soldering equipment and materials. The solder in this picture is coiled inside a plastic tube; it is pulled through the top as needed. The spring on the stand holds the hot soldering iron. The damp sponge is used to clean the tip of the iron. Solder braid is used to remove solder; solder is "soaked up" into the braid when it is heated by the soldering iron. The wire strippers can be adjusted to strip the plastic covering off of various thicknesses of wire. The prototype board is used to connect electronic components in a circuit.

Solder braid

This is used to remove solder.

To use the braid, place it over the solder to be removed and heat it from above with the iron. The solder will flow into the braid.

Solder braid is used to extract an electronic component that is soldered onto a board.

You can find this page online at: https://www.sciencebuddies.org/science-fair-projects/references/how-to-solder

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